1051-232-20033 Imaging Systems Laboratory II Week of 5/3/2004, Writeup Due 5/18/2004 (T)
1 Laboratory 8: Michelson Interferometer 1.1 Theory: References:Optics,E.Hecht,sec 9.4
1.1.1 Division-of-Wavefront Interferometry In the last lab, you saw that coherent (single-wavelength) light from point sources two different locations in an optical beam could be combined after having traveled along two different paths. The recombined light exhibited sinusoidal fringes whose spatial frequency depended on the difference in angle of the light beams when recombined. The regular variation in relative phase of the light beams resulted in constructive interference (when the relative phase difference is 2πn,wheren is an integer) and destructive interference where the relative phase difference is 2πn + π. The centers of the “bright” fringes occur where the optical paths differ by an integer multiple of λ0.
“Division-of-Wavefront” Interferometry via Young’s Two-Slit Experiment. The period of the intensity fringes at the observation plane is D Lλ . ' d
1.1.2 Division-of-Amplitude Interferometry This laboratory will introduce a second class of interferometer where the amplitude of the light is separated into two (or more) parts at the same point in space via partial reflection by a beamsplitter. The beamsplitter is the light-dividing element in several types of interferometers. This lab will demostrate the action of the Michelson interferometer for both coherent light from a laser and for white light (with some luck!).
Coherence of a Light Source If two points within the same beam of light exhibit a consistent and measurable phase difference, then the light at the two points is said to be coherent, and thus
1 the light at these two locations may be combined to create interference. The ease with which fringes can be created and viewed is determined by the coherence of the source. The coherence length is the difference in distance travelled by two beams of light such that they generate detectable interference when recombined. The coherence time is the time period that elapses between the passage of these two points that can “just” interfere: